The present invention relates to hydraulic systems for transmitting power from an internal combustion engine to the wheels of a motor vehicle, of the type having:
a variable-output reversible hydraulic pump,
a mechanical transmission between the internal combustion engine and the hydraulic pump,
control means for varying the output of the hydraulic pump,
a variable-output hydraulic motor designed to be used reversibly as a pump,
a further mechanical transmission for connecting the hydraulic motor to the wheels of the vehicle.
control means for varying the output of the hydraulic motor,
a delivery conduit connecting the outlet of the hydraulic pump to the inlet of the hydraulic motor and
a return conduit connecting the outlet of the hydraulic motor to the inlet of the hydraulic pump.
The hydraulic transmission may be of the hydrostatic or hydrodynamic type.
The object of the present invention is to provide an hydraulic transmission system for a motor vehicle of the type specified above which allows, at least some of the kinetic energy dissipated during deceleration of the vehicle to be recovered and re-used to power the subsequent rotation of the vehicle wheels so as to enable the internal combustion engine to operate almost constantly under its most efficient working conditions.